For large pipe lines large gates valves are known having a body manufactured from steel plates which are welded together to obtain two parallel flat end walls and two side walls such that in a plane perpendicular to said end walls, a rectangular cross section is obtained. Said end walls are provided with aligned openings to form flow passages, and hubs and pipe sections can be placed in line with said openings for making the connection with associated piping. The valve body of said gate valves is formed by a plate slidable between annular seals which are concentric with the flow passages, said plate having an opening which can be brought in line with the flow passages or can be closed by another portion of said plate. This structure of the valves requires a large valve body the walls of which being subjected to the loads resulting from the pressure in the piping, in particular, from the pressure shocks which can occur upon closing the valve and the high pressure to be held in the closed condition. This requires very rigid end walls and to this end it is well known to provide the end walls with reinforcing ribs extending across the exterior faces of said end walls and in engagement therewith which ribs are placed in parallel planes, the ribs on both sides of the body present in a common plane being interconnected by side strips, the outer ends of which are welded to the ribs and which themselves are welded to the side walls.
An example of such gate valve is shown in U.S. Pat. No. 3,260,503. Another example is shown in U.S. Pat. No. 3,638,908.
Gate valves of this type are large heavy bodies which have to fulfill safety prescriptions in particular with respect to the weldings.
The manufacturing of the known gate valve constructions is difficult and time consuming and a number of welding seams of said known constructions do not allow proper and complete examination. In a welding construction of this size it always is difficult and requires skill to keep the tensions within the material resulting from the welding process in acceptable limits.